This invention relates to a telecommunications interface for personal computers (PCs) that allows the PC to act as a terminal for telecommunications signalling that complies with Bellcore specification TR-TSY-000030, popularly known as CLASS (trade-mark).
There are many types of telephone services available. The most basic service is called POTS (Plain Old Telephone Service) and is typically associated with residential and small business users. The general service offering for businesses, popularly called CENTREX, provides services such as Call Forwarding and Call Waiting through the use of proprietary control channels. ISDN (trade-mark) (Integrated Services Digital Network) provides combined voice, data, and control channels using nonproprietary signalling. CLASS (Custom Local Area Signalling Services) provides a nonproprietary control channel so that services normally associated with CENTREX can be provided to residential and small business customers.
The general signalling scheme used by CLASS was first described in U.S. Pat. No. 4,551,581, the basic AT&T CLASS patent. It describes a method of delivering the required signalling during the silent period of the ring cycle. The first application of this signalling to customer premises equipment (i.e. CLASS CPE) is taught in Canadian patent 1,225,726, filed Jul. 12, 1983 entitled "Method and Apparatus for Displaying at a Selected Station Special Service Information During a Silent Interval Between Ringing". This patent deals with apparatus capable of delivering the incoming signalling information in a format that may be interpreted by humans. The subject of the present patent is an interface for delivering the incoming signalling information in a format that may be interpreted by a computer system. The marketplace forced an industry wide consensus on the specifications to be used by the signalling channel, from the Customer Premise Equipment (CPE) viewpoint, to be developed. It is given in Bellcore Technical Reference TR-TSY-000030, "SPCS Customer Premises Equipment Data Interface", Issue 1, November, 1988.
The marketplace has also brought forward a number of other implementations of CPE for CLASS designed for human use, both in the form of fully featured, highly intelligent telephone sets and in the form of adjunct units to existing telephones, containing alphanumeric or numeric displays and function keys to take advantage of the new features.
None of the existing or proposed systems provide an interface device for connecting a PC to the network using CLASS signalling. U.S. Pat. No. 4,748,656 teaches the use of a PC as an interface between a telephone and a business communications system with the PC terminating both the telephone set and the business communications system but it is a system that operates in serial fashion--the business communications system to the PC to the telephone. The invention described by this patent operates in parallel with the telephone--the business communications system to the PC and the telephone at the same time. Also, the signalling format used in U.S. Pat. No. 4,748,656 is proprietary and differs from the specifications set out in Bellcore TR-TSY-000030.
U.S. Pat. No. 4,776,005, "Computer Based Information System For Character Display Phone Network" teaches the use of a PC to enhance the functionality of a multi-line PBX display telephone to allow it to be used as the heart of a messaging system (i.e. one operator/receptionist for up to hundreds of numbers). While the intent of the present patent and this system are somewhat similar, the present patent provides a computer interface for a different type of signalling than that used by U.S. Pat. No. 4,776,005.
One drawback of telephone sets that comply with Bellcore specification TR-TSY-000030 is the complexity of the required circuitry. This circuitry requires larger amounts of electrical power than classic telephone sets and, for some features, must be independent of power supply failure from the telephone switch. These requirements force CLASS sets to have either internal batteries or an external power supply--both of which are impediments to acceptance in the marketplace.
The most cost effective method of implementing the invention is to power it from the computer interface or the telephone line, thus eliminating the need for a separate power supply. If computing platform independence is not required, the invention can be implemented as a card that plugs into an internal slot. However, if the invention is to be powered from the computer interface then, since all computers do not have the same internal interfaces, it is desirable to implement the invention in a manner that will derive power from a standard external interface. Canadian Patent No. 1192644 teaches a method of deriving power from the terminal interface for a data communications apparatus. U.S. Pat. No. 4,543,450 teaches the integration of connector and modem that derives power through at least one pin of the connector.
Alternatively, U.S. Pat. No. 4,578,533 teaches a method of extracting power from the telephone line to power a modem for data communications.
However, deriving power solely from either source is very unlikely to be sufficient to provide the power necessary for proper functioning of the invention. Not only would the requirements for energy storage (in capacitors) force an uneconomical solution but the reliability of the system in power failure conditions would be unacceptable. A combination of the two approaches, however, would be able to provide the necessary power with an acceptable level of reliability.
For purposes of discussion, the external implementation will be the preferred embodiment because it is independent of the computing platform. In all discussions of embodiments, the essential elements of the invention, not including the power supply mechanism, are the same for the internal and external implementation.
In summary, existing mechanisms for utilizing telecommunications signals, transmitted according to the format specified in Bellcore TR-TSY-000030, are for conventional telephone sets for human use. These devices take the form of fully featured, highly intelligent telephone sets or as adjunct display units that work in parallel with existing telephones. The capabilities of these systems are hampered by their need to be cost competitive with conventional telephone sets and to draw their power from the telephone network, and internal batteries or an external power supply. The invention presented herein is, effectively, a telephone set for a computer. The invention takes advantage of the greater intelligence of the computer to provide a system of greater functionality and ease of use than existing systems. The power supplies of the computer and the telephone network are used to provide the extra power requirements with an acceptable level of reliability.